Engines in which gasoline is used as a fuel, motors driven by electricity, and hybridized engine/motor combinations are used as power sources in automotive vehicles. Recently, fuel cell vehicles, in which a motor that is driven using electricity generated by a fuel cell, have been attracting attention due to environmental considerations. A fuel cell is an apparatus that supplies air and hydrogen to a membrane electrode assembly configured having an anode and a cathode with an electrolyte membrane interposed therebetween to generate electrical energy and water. The following method has been proposed for manufacturing membrane electrode assemblies employed in such fuel cells.
As shown in FIG. 5A, a mask 101 that has been cut to a predetermined shape is disposed on a substrate 100, and as shown in FIG. 5B, an electrode layer paste 102 to become an electrode layer is applied to the substrate 100. The substrate 100 and mask 101 covered with the electrode layer paste 102 are placed inside a dryer, and dried at a predetermined temperature. The drying causes the electrode layer paste 102 to solidify.
Next, the mask 101 is peeled from the substrate 100. As shown in FIG. 5C, a solid electrode layer 103 of predetermined shape is obtained. At this point, when the mask 101 is peeled from the substrate 100 after the electrode layer paste 102 has solidified, sharply peaked protuberant configurations 104 are formed on the outer peripheral edge of the electrode layer 103.
As shown in FIG. 5D, the electrode layer 103 is transferred to one surface of an electrolyte membrane 105 using thermocompression bonding. A membrane electrode assembly is obtained by transferring an electrode layer in the same way to the other surface of the electrolyte membrane 105 using thermocompression bonding, and forming gas diffusion layers on the electrode layers on the both surfaces [of the electrolyte membrane 105. However, when the electrode layer 103 on which the protuberant configurations 104 are formed is transferred to the electrolyte membrane 105, the protuberant configurations 104 penetrate the electrolyte membrane 105 and damage the electrolyte membrane 105. Various methods for manufacturing membrane electrode assemblies that address such drawbacks have been proposed (e.g. Japanese Patent Application Laid-Open Publication No. 2014-67483).
As shown in FIG. 6A, a rectangular substrate 110 is prepared, and as shown in FIG. 6B, a mask 111 that has been cut in a predetermined shape is disposed on the substrate 110. As shown in FIG. 6C, an electrode layer paste 112 is applied to the substrate 110, and as shown in FIG. 6D, partial drying is performed by leaving the substrate 110 in a hot chamber to make the electrode layer paste 112 a semi-solid. Partial drying is performed so that that electrode layer paste 112 will have sufficient viscosity to retain its shape when the mask is removed. As shown in FIG. 6E, the mask 111 is peeled from the substrate 110 while the electrode layer paste 112 impregnated with a solvent is wet. By removing the mask 111, the outer peripheral edge part of the electrode layer paste 112 is also removed, and the electrode layer paste 112 assumes the desired shape.
As shown in FIG. 7, the outer peripheral edge part 113 of the electrode layer paste 112, being in a partially dry state, flows toward the outer periphery under gravity, and slants to a taper so as to decrease in thickness toward the outer periphery.
Next, as shown in FIG. 6F, the electrode layer paste 112 is placed in a dryer 114 together with the substrate 110 and fully dried, and, as shown in FIG. 6G, an electrode layer 115 that has formed into a solid on the substrate 110 is obtained. As shown in FIG. 6H, substrates 110, 110 having the electrolyte membrane 116 therebetween are thermocompression bonded by a press machine 118 so that the electrode layer 115 on the anode side and an electrode layer 117 on the cathode side make contact with the electrolyte membrane 116. As shown in FIG. 6I, peeling the substrates 110, 110 from the electrode layers 115, 117 yields an electrolyte membrane 116 on which the electrode layers 115, 117 are disposed on both surfaces.
However, because the mask 111 is removed while the electrode layer paste 112 is wet (semi-solid), the outer peripheral edge of the electrode layers 115, 117 may change slightly in shape. Accordingly, a method is required for manufacturing a membrane electrode assembly that enables the shape of the electrode layer to be formed accurately without mechanically damaging the electrolyte membrane.